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From: Yuyang Du <duyuyang@gmail.com>
To: peterz@infradead.org, will.deacon@arm.com, mingo@kernel.org
Cc: bvanassche@acm.org, ming.lei@redhat.com, frederic@kernel.org,
	tglx@linutronix.de, boqun.feng@gmail.com,
	linux-kernel@vger.kernel.org, Yuyang Du <duyuyang@gmail.com>
Subject: [PATCH 17/17] locking/lockdep: Remove irq-safe to irq-unsafe read check
Date: Mon, 13 May 2019 17:12:03 +0800	[thread overview]
Message-ID: <20190513091203.7299-18-duyuyang@gmail.com> (raw)
In-Reply-To: <20190513091203.7299-1-duyuyang@gmail.com>

We have a lockdep warning:

  ========================================================
  WARNING: possible irq lock inversion dependency detected
  5.1.0-rc7+ #141 Not tainted
  --------------------------------------------------------
  kworker/8:2/328 just changed the state of lock:
  0000000007f1a95b (&(&host->lock)->rlock){-...}, at: ata_bmdma_interrupt+0x27/0x1c0 [libata]
  but this lock took another, HARDIRQ-READ-unsafe lock in the past:
   (&trig->leddev_list_lock){.+.?}

and interrupts could create inverse lock ordering between them.

other info that might help us debug this:
   Possible interrupt unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&trig->leddev_list_lock);
                                 local_irq_disable();
                                 lock(&(&host->lock)->rlock);
                                 lock(&trig->leddev_list_lock);
    <Interrupt>
      lock(&(&host->lock)->rlock);

 *** DEADLOCK ***

This splat is a false positive, which is enabled by the addition of
recursive read locks in the graph. Specifically, trig->leddev_list_lock is a
rwlock_t type, which was not in the graph before recursive read lock support
was added in lockdep.

This false positve is caused by a "false-positive" check in IRQ usage check.

In mark_lock_irq(), the following checks are currently performed:

   ----------------------------------
  |   ->      | unsafe | read unsafe |
  |----------------------------------|
  | safe      |  F  B  |    F* B*    |
  |----------------------------------|
  | read safe |  F* B* |      -      |
   ----------------------------------

Where:
F: check_usage_forwards
B: check_usage_backwards
*: check enabled by STRICT_READ_CHECKS

But actually the safe -> unsafe read dependency does not create a deadlock
scenario.

Fix this by simply removing those two checks, and since safe read -> unsafe
is indeed a problem, these checks are not actually strict per se, so remove
the macro STRICT_READ_CHECKS, and we have the following checks:

   ----------------------------------
  |   ->      | unsafe | read unsafe |
  |----------------------------------|
  | safe      |  F  B  |      -      |
  |----------------------------------|
  | read safe |  F  B  |      -      |
   ----------------------------------

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 kernel/locking/lockdep.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 69d6bd6..62b454c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3446,8 +3446,6 @@ static int SOFTIRQ_verbose(struct lock_class *class)
 	return 0;
 }
 
-#define STRICT_READ_CHECKS	1
-
 static int (*state_verbose_f[])(struct lock_class *class) = {
 #define LOCKDEP_STATE(__STATE) \
 	__STATE##_verbose,
@@ -3493,7 +3491,7 @@ typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
 	 * Validate that the lock dependencies don't have conflicting usage
 	 * states.
 	 */
-	if ((!read || STRICT_READ_CHECKS) &&
+	if ((!read || !dir) &&
 			!usage(curr, this, excl_bit, state_name(new_bit & ~LOCK_USAGE_READ_MASK)))
 		return 0;
 
@@ -3504,7 +3502,7 @@ typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
 		if (!valid_state(curr, this, new_bit, excl_bit + LOCK_USAGE_READ_MASK))
 			return 0;
 
-		if (STRICT_READ_CHECKS &&
+		if (dir &&
 			!usage(curr, this, excl_bit + LOCK_USAGE_READ_MASK,
 				state_name(new_bit + LOCK_USAGE_READ_MASK)))
 			return 0;
-- 
1.8.3.1


  parent reply	other threads:[~2019-05-13  9:14 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-13  9:11 [PATCH 00/17] Support for read-write lock deadlock detection Yuyang Du
2019-05-13  9:11 ` [PATCH 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks Yuyang Du
2019-05-13 11:45   ` Peter Zijlstra
2019-05-14  1:31     ` Yuyang Du
2019-05-14 12:04       ` Peter Zijlstra
2019-05-13  9:11 ` [PATCH 02/17] locking/lockdep: Add read-write type for dependency Yuyang Du
2019-05-13  9:11 ` [PATCH 03/17] locking/lockdep: Add helper functions to operate on the searched path Yuyang Du
2019-05-13  9:11 ` [PATCH 04/17] locking/lockdep: Update direct dependency's read-write type if it exists Yuyang Du
2019-05-13  9:11 ` [PATCH 05/17] locking/lockdep: Rename deadlock check functions Yuyang Du
2019-05-13  9:11 ` [PATCH 06/17] locking/lockdep: Adjust BFS algorithm to support multiple matches Yuyang Du
2019-05-13  9:11 ` [PATCH 07/17] locking/lockdep: Introduce mark_lock_unaccessed() Yuyang Du
2019-05-13  9:11 ` [PATCH 08/17] locking/lockdep: Introduce chain_hlocks_type for held lock's read-write type Yuyang Du
2019-05-13  9:11 ` [PATCH 09/17] locking/lockdep: Hash held lock's read-write type into chain key Yuyang Du
2019-05-13  9:11 ` [PATCH 10/17] locking/lockdep: Support read-write lock's deadlock detection Yuyang Du
2019-05-13  9:11 ` [PATCH 11/17] locking/lockdep: Adjust lockdep selftest cases Yuyang Du
2019-05-13  9:11 ` [PATCH 12/17] locking/lockdep: Remove useless lock type assignment Yuyang Du
2019-05-13  9:11 ` [PATCH 13/17] locking/lockdep: Add nest lock type Yuyang Du
2019-05-13  9:12 ` [PATCH 14/17] locking/lockdep: Support recursive read locks Yuyang Du
2019-05-13  9:12 ` [PATCH 15/17] locking/lockdep: Adjust selftest case for recursive read lock Yuyang Du
2019-05-13  9:12 ` [PATCH 16/17] locking/lockdep: Add more lockdep selftest cases Yuyang Du
2019-05-13  9:12 ` Yuyang Du [this message]
2019-05-13  9:17 ` [PATCH 00/17] Support for read-write lock deadlock detection Yuyang Du

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